Prior art chairs of similar type intended for use by persons suffering from different handicaps, especially spasticity, exhibit seats, which can be brought into different angular positions with the aid of various piston-cylinder arrangements. In this type of adjustment devices the piston movement in the cylinder is controlled by means of a manually operated valve and the device functions against a spring means continuously striving to tilt the seat into a position inclined forwards or backwards in response to the structural arrangement of the device. The most usual arrangement is that the structure with the aid of the spring member holds the seat in a forwards inclined position, which is altered when the control cylinder device is opened-by means of a lever and a person sits down on the seat. The angular position is then changed to an outer end position, somewhat inclined backwards. By actuation of the control lever for the cylinder device the seat can be brought into a desired position yielding a comfortable seating, the seat being then by the spring automatically tilted forwards into the position corresponding to release of the control lever for the piston-cylinder device. However, this technical solution has proved inconvenient to persons suffering from certain types of handicap, particularly spasticity. If the control lever is not handled correctly the result may be that the person can actually fall out from the chair.